This invention relates to an oceanography probe, which is a device for recording information relating to ocean water such as temperature or salinity at various depths and more particularly to an improved expendable oceanography probe.
In the past, for example, for measuring the temperature of water as a function of depth, it was a common practice to sink and raise a thermometer attached to a line and to record the temperature of the water. But, it is difficult to read an indication and record the temperature on a vessel moving at the sea. In order to overcome such a problem, an expendable bathythermograph system and oceanography probe are widely used. For example, U.S. Pat. Nos. 3,221,556 and 3,339,407 disclose an expendable ballistic bathythermograph system and an oceanography probe unit which provide a temperature-depth profile as the probe containing a thermometer and separated from the probe unit falls through the water. Then the probe is abandoned at the bottom of the sea.
The probe unit of the above mentioned expendable bathythermograph system comprises a probe container, a probe, a thermistor and two spools of wire. One of the two spools of wire and the thermistor are provided in the probe and the thermistor is connected to the wire of this spool. The other of the two spools is mounted in the probe container on the vessle. When the probe is dropped, wire is unwound from both the spools, and the probe can fall nearly straight through the water. As the probe falls through the water, the thermistor in the probe sends out signals to the vessel which are responsive to the temperature of the water. When the wires are played out, the wires break and the probe sinks freely to the bottom of the sea. This system provides some advantages as compared with a thermometer attached to a line, since it may be used even while the vessel moves at sea. Further, as the probe may be made at a low cost, it may be thrown away. However, the wire is awkward to use, and in addition, the wire affects the rate of speed at which the probe falls and the direction which probe falls through the water, and the operating depth for the probe is limited by the length of the wire.
So as to overcome these problems, for example as disclosed in U.S. Pat. No. 3,561,268, an expendable wireless bathythermograph system has been designed to take the temperature-depth profile of the water from the vessel which moves at sea. This probe includes a free-falling underwater body which has a streamlined hull characteristic that produces a stable rate of fall through the water, an oscillator connected to piezoelectric hollow cylindrical transducer for radiating sound waves through the water at the oscillator output frequency, and two sensors which alter the oscillator output frequency as a function of depth and temperature. A receiver on the surface of the water receives the radiated sound waves and prints out the temperature and depth of the water through which the probe is passing. Such a wireless device has advantages as compared with the above-mentioned wire expendable bathythermograph, since the probe is a wireless free-falling body radiating the under water sound signals which vary frequencies with the temperature and the depth.
However, it is difficult to make the dimensions and the contour of the piezoelectric ceramic cylindrical ring so as to provide the streamlined shape of the probe. Since the outside diameter of the piezoelectric ceramic ring transducer is generally in the range of 1.5 to 2 inches and the height of the ring transducer is about 0.5 to 1.25 times the outside diameter, the transducer with the desired shape of a piezoelectric ceramic ring body often causes a lot of unwanted responses, which are easily piezoelectrically excited by the oscillator in the probe, with respect to the frequency characteristic of the ring transducer. Further, it is difficult to control the transmission pattern of sound waves from the probe into the surrounding water, since the transmission pattern of sound waves depends on the vertical height of the ceramic ring and the wave lengths of the radiated sounds.